The present invention relates to an IC card system wherein security in regard to confidentiality of data stored in an IC card can be improved when a test program stored in an IC circuit in the card is started.
Our contemporary age is called a "cashless" age, and customers frequently use credit cards issued by credit companies to purchase desired items without cash transactions.
Conventional cards of this type are a plastic card, an embossed card, and a magnetic stripe card. These cards can be easily counterfeited due to their structural problems, and illegal use of these cards has become an issue.
An information card incorporating an IC circuit for storing an identification number or the like therein, that is, an IC card is proposed to solve the above problems.
Various types of LSIs such as a data memory and a system program ROM are incorporated in such an IC card. In this case, addressing and read/write access of the data memory and the bit pattern status of the system program ROM must be controlled to be normal. For this purpose, IC cards must be tested to check their states at the end of assembly of the cards and during use thereof.
In a conventional IC card, a test program is stored in an IC chip and a predetermined test can be executed externally through test terminals on the card.
However, simple external testing through the test terminals also indicates easy extraction of confidential information such as bit patterns of the system program ROM and the data memory. This means that a card can be counterfeited on the basis of the extracted information, and that, in the worst case, techniques in a system using IC cards may be analyzed and illegally used in a large scale.
Even if a test program in the IC card is legally initialized and executed, errors in LSIs during various tests are detected as card errors. In this sense, it is difficult to specify the error location, and a proper countermeasure cannot be taken against this error. As a result, even if a simple error occurs, the entire IC card must be discarded.